DESCRIPTION (adapted from abstract): This proposal focuses on elucidation of the molecular, pharmacological and regulatory properties of an important K+ channel which is believed to be an essential repolarizing current during the cardiac action potential. As such, this particular delayed rectifier K+ channel, IKs, represents an important target site for several new class III antiarrhythmic agents. The applicant proposes to test the hypothesis that alterations in the genetic message encoding this channel may be directly responsible for at least one type of potentially lethal idiosyncratic drug response to class III agents observed in a small percentage of otherwise healthy patients. The specific aims of the proposal include: (1) to measure and compare the biophysical properties of native and recombinant forms of IKs to determine whether or not the minK gene encodes an ion channel protein or instead represents a regulator or cofactor of an unidentified protein responsible for IKs in native cardiac cells and heterologous expression systems, (2) to test the hypothesis that a single amino acid mutation in minK (A112G) recently discovered by the applicant to be a polymorphism of the human minK gene, changes the sensitivity of expressed minK channels to the class III antiarrhythmic drug, NE-10064, by identifiable changes in expressed channel structure, and (3) to investigate the expression of native and recombinant forms of IKs in wild type and genetically altered murine embryonic cells and stem cell derived cardiocytes to study the developmental regulation of functional minK channels in mammalian heart. This last specific aim will test the hypotheses that expression of functional minK channels in the developing heart is regulated by the beta-adrenergic signaling cascade, and that the presence of message for minK alone in early stage murine embryonic cells is insufficient to cause expression of functional minK channels. The results of these studies should provide the most detailed description to date of the molecular and genetic properties of IKs and its relevance to human cardiovascular pharmacology and disease.